British Pat. No. 1,360,009 disclosed inter alia certain compounds having cardiovascular and central nervous system activity. These compounds included those of the formula (II): ##SPC2##
wherein A.sub.1 was an aliphatic group of 1 - 20 carbon atoms, A.sub.2 is an optionally substituted hydrocarbon group of 1 - 20 carbon atoms.
U.S. patent application Ser. No. 324,222, U.S. Pat. No. 3,853,899 diclosed the excellent antihypertensive activity of compounds including those of the formula (III): ##SPC3##
wherein R.sub.3 is an alkyl group of 5 - 8 carbon atoms, n is 1 or 2 and A.sub.4 is a phenyl or naphthyl group.
Compounds of formulae (II) and (III) are now believed to represent classes of potentially very useful antihypertensive agents. However it has now been found that certain related compounds (of formula (I) as discussed below) have anti-hypertensive activity at least as good as the compounds of formula (II) or (III) specifically prepared in the above mentioned patent specifications and also possess the surprising advantage of a considerably improved therapeutic ratio especially with regard to renal toxicity. No certain explanation for this improvement can as yet be postulated but the advantages of the new compounds have been confirmed by repeated experimentation.